According to (Pinel, 2009, P. 432) Darwin’s theory of emotion consist of his believe that human facial expressions tend to accompany the same emotional states in all species, and that expressions of emotions are products of evolution. He believed that expressions of emotions can indicate what an animal is likely to do next, that if this signals work in favor for the animal that they will evolve to enhance communication, and that opposite messages are shown by opposite movements such as looking away when showing submission. And looking at someone directly in the face when showing aggression.
In James-Lange theory of emotion he believed that first we face the perception of experience then we have physiological reactions that lead to the result of our emotions. For example we have the perception of a angry dog while walking to the park, we start running then we feel emotions of fear once we have already started running away from the angry dog (Pinel, 2009, P. 433).
In Cannon-Bard theory of emotion he believed that after a perception experience we face both emotional experience and emotional expression at the same time with no direct casual relation. In the case of the angry dog experience it would be that after seeing the angry dog, the person started running with fear away from the dog. Neither running or the emotion of fear started first, they both did at the same time (Pinel, 2009, P. 433-434).
According to (Pinel, 2009, P. 435) emotional expression is believed to be controlled by several interconnected neural structures, the limbic system, which is a collection of nuclei and tracts that border the thalamus. These structures include the amygdala, mammillary body, hippocampus, fornix, cortex of the cingulate gyrus, septum, olfactory bulb, and hypothalamus. Papez believed that emotional states are expressed through actions of limbic structures in the hypothalamus and that they are experienced through actions of limbic structures in the cortex.
References: Pinel, J. P. J. (2009). Biopsychology. Boston, MA: Pearson.